Block2 1.er-Golgi I

Front 1

Signal Hypothesis

Back 1

Signal recognition particle binds, it stalls translation 
so secondary structures don't form yet. Know there's an SRP receptor in the membrane. Both the SRP and the SRP receptor bind GTP, hydrolysis causes associated translocon to open. A translocon membrane protein is the passageway into the cell, the protein literally gets pumped into the cell as it is being translated by the ribosome. A signal peptidase cleaves the signal sequence off of the protein

Front 2

BiP

Back 2

ER protein involved in unidirectional transport of protein being translated. Sec63 complex promotes BiP hydrolyzing its bound ATP to ADP. The ADP-bound form grasps translocating proteins and pulls them inward to the ER lumen

Front 3

ER membrane insertion:
Type I

Back 3

One pass, signal sequence is cleaved, COO- out in the cytosol, NH3+ in the ER lumen. The Stop Transfer Anchor Sequence is a seuqence made up of hydrophobic aa's that gets passed laterally through the pore protein and embeds in the membrane, becoming the membrane domain of the newly translated protein

Front 4

Type II Membrane Insertion

Back 4

Single pass, signal sequence NOT CLEAVED. The COO- is inside ER lumen, the NH3+ outside in the cytosol. Signal Anchor Sequence: has positive charges flanking this region. These will always end up on the cytosolic side= (in type II, NH3+ gets put on outside, so the charges are on that side)

Front 5

Type III Membrane insertion

Back 5

Single pass, same as Type I except the signal sequence NOT CLEAVED and the presence of Signal Anchor Sequence, containing the positive charges flanking the COO- side (causing that side to be in the cytosol)

Front 6

Type IV Membrane insertion

Back 6

Multi-pass. Odd number of membrane domains means the terminals are on opposite sides of membrane, even number they are on same side

Front 7

GPI-Anchored Proteins and GPI transamidase

Back 7

Imagine inserted protein. The GPI transamidase takes the COO- and attaches it the GPI anchor, which is on interior half of ER membrane. When excreted from Golgi later, the protein will be facing out of the cell in the plasma membrane

Front 8

Glycosylation

Back 8

Process going on in ER, usually aiming protein at Golgi. Protein folding, targeting, stability, cell-cell
interactions (lectins). Two types: O-linked and N-linked

Front 9

O-linked Glycosylation

Back 9

Carbohydrates added sequentially to –OH group of Ser or Thr by Glycosyl transferases in Golgi. ABO blood groups.

Front 10

N-linked Glycosylation

Back 10

The oligosaccharide to be added is pre-formed before it is put on. It is a big bulky thing that is always added to Asn in a sequence like this: NH3+--X--Asn--X--Ser/Thr--COO-

Front 11

Synthesis of Oligosaccharide Precursor and Tunicamycin

Back 11

In the first, rate limiting step of the creation of the oligosaccharide for N-linked glycosylation, and ONLY this step, a diphosphate nucleotide to hydrolyzed. Tunicamycin blocks this from happening

Front 12

Protein Disulfide Isomerase (PDI)
Disulfide Bond Formation and Ero1

Back 12

PDI itself has a disulfide bond that it transfers to a molecule. Ero1 does the same thing for PDI in order to regenerate it; oxidized Ero-1 can transfer its disulfide bond to PDI.
PDI can also help in the rearrangement of existing disulfide bonds

Front 13

Proper Protein Folding: Coordinated Process

Back 13

Coordinated functions: Oligosaccharyl transferase, chaperones
(BiP), sugar-binding Lectins (Calnexin and Calreticulum), PDI
mediate glycosylation, disulfide bond formation, proper folding
and subunit assembly.

Front 14

Alpha-1 Antitrypsin Deficiency and elastase

Back 14

A-1AT is an enzyme produced in liver that inhibits elastase activity in the lungs. A mutation causes improper folding and the enzyme never gets out of liver. This causes lung deterioration and liver problems due to the build up of residues and other things that get stuck in there as a result